The thermodynamic dissociation constants of four non-steroidal anti-inflammatory drugs by the least-squares nonlinear regression of multiwavelength spectrophotometric pH-titration data

The mixed dissociation constants of four non-steroidal anti-inflammatory drugs (NSAIDs) ibuprofen, diclofenac sodium, flurbiprofen and ketoprofen at various ionic strengths I of range 0.003-0.155, and at temperatures of 25 degrees C and 37 degrees C, were determined with the use of two different multiwavelength and multivariate treatments of spectral data, SPECFIT/32 and SQUAD(84) nonlinear regression analyses and INDICES factor analysis. The factor analysis in the INDICES program predicts the correct number of components, and even the presence of minor ones, when the data quality is high and the instrumental error is known. The thermodynamic dissociation constant pK(a)(T) was estimated by nonlinear regression of (pK(a), I) data at 25 degrees C and 37 degrees C. Goodness-of-fit tests for various regression diagnostics enabled the reliability of the parameter estimates found to be proven. PALLAS, MARVIN, SPARC, ACD/pK(a) and Pharma Algorithms predict pK(a) being based on the structural formulae of drug compounds in agreement with the experimental value. The best agreement seems to be between the ACD/pK(a) program and experimentally found values and with SPARC. PALLAS and MARVIN predicted pK(a,pred) values with larger bias errors in comparison with the experimental value for all four drugs.     

The use of derivative and least-squares methods to analyse a polypharmaceutical product by UV spectrophotometry

Derivative UV spectrophotometry is well established for analysing pharmaceutical products containing more than one drug. By contrast, the least-squares method for over-determined systems is rarely used, because it is assumed that measurements at a large number of wavelengths are needed to obtain good results. Both methods have advantages, and their use in combination is useful for analysing polypharmaceuticals. A combination of derivative and least-squares methods was used to analyse tablets containing pseudoephedrine hydrochloride, triprolidine hydrochloride and dextromethorphan hydrobromide. Pseudoephedrine was determined by derivative spectrophotometry. The other drugs were determined by the least-squares method at higher wavelengths where pseudoephedrine does not absorb. Satisfactory precision for the least-squares method was obtained with a manual spectrometer measuring at six wavelengths and calculating the results with a microcomputer.     

Partial characterization of different mixtures of solids by measuring the optical nonlinear response

We report on the theoretical basis and first experimental results of a new method based on optical nonlinearity, for characterising crystallinity and polymorphism of pharmaceuticals in the solid state. Once the theoretical basis of optical nonlinearity of crystalline structures is established, a new and rapid method based on this physical theory can be developed to quantitatively determine polymorphism or crystallinity. An apparatus was set up to measure the second harmonic response of powdered samples when irradiated with a pulsed laser source. The response of quartz-glass, enalapril maleate forms I-II and enalapril maleate form II-PVP mixtures were measured and modeled. It was found that the quartz-glass system showed high sensitivity to the presence of quartz and was well predicted by our theoretical model. The response of enalapril maleate polymorph mixtures was also sensitive to changes in the polymorph ratio. The theoretical predictions of the polymorph mixtures agreed quantitatively with the experimental results. The response of enalapril maleate form II-PVP mixtures agreed quantitatively with the physical model and showed extremely low noise and high sensitivity, giving very promising limits of detection (LOD) and quantification (LOQ) of 0.12 and 0.41%, respectively. This rapid, novel technique has potential for industrial monitoring of pharmaceutical manufacturing processes.     

Meta analysis of advanced cancer survival data using lognormal parametric fitting: a statistical method to identify effective treatment protocols

We describe the use of a parametric lognormal model to calculate and compare survival statistics in the clinical treatment of advanced/metastatic pancreatic, breast and colon cancers. The fit using the lognormal model explained greater than 90% (R(2) ranged from 0.917 to 0.998 for a total of the 51 arms from published studies) of the variation in the cumulative survival statistics of patients treated for advanced cancers. A meta-analytic Q-test was performed to test whether there were significant differences between different studies. For all three cancer types, the Q-test showed highly significant differences between the survival arms (p<0.0001 for pancreatic, breast and colon cancers). The z-values expressed the difference of the average of lognormal means relative to each study in terms of deviation expressed in standard errors. The treatments that were most effective ranked with the highest z-value: Doxorubicin plus docetaxel for pancreatic cancer (z-value = 4.1); Capecitabine plus paclitaxel for breast cancer (z-value = 3); irinotecan, fluorouracil and folinate for colon cancer (z-value = 7.4).     

Freundlich and Langmuir isotherms as models for the adsorption of toxicants on activated charcoal

The Langmuir isotherm has been widely used to characterize the adsorption of solutes from aqueous solutions. Activated charcoal adsorption data obtained experimentally, using a wide range of adsorbate concentrations, fit the Langmuir isotherm poorly but evidence a good fit to the Freundlich isotherm. Statistical analysis reveals this to be also true of published data that was previously considered to adhere to the Langmuir isotherm. Over the range of possible adsorbate concentrations, the two isotherms predict rather different adsorption behavior. Of the two, the Freundlich isotherm is able to more fully account for observed antidotal effectiveness of activated charcoal in vivo. A method of graphical analysis is advanced that more readily distinguishes the relative goodness-of-fit of the two isotherms. This and the statistical paradigm employed to decide between the two competing hypotheses should allow the adsorption phenomena involving other adsorbents to be re-examined.     

Use of a nonlinear least-squares model for the kinetic determination of the stability constant of cyclodextrin inclusion complexes

The nonlinear least-squares model for the calculation of the stability constants (K_st) of drug:cyclodextrin complexes was used in kinetic studies. Complexation of riboflavin (R) with hydroxypropyl-β-cyclodextrin (HP:β-CD) was monitored kinetically by measuring the rate of photodegradation of R exposed to ultraviolet light in the presence of increasing concentrations of HP:β-CD. Formation of inclusion complex was confirmed in aqueous solution by proton nuclear magnetic resonance spectroscopy (¹H-NMR). The experimental K_st value (3321 M⁻¹), derived from the kinetic studies, appeared to fit well to a 1:1 drug: cyclodextrin molar ratio according to the nonlinear mathematical model. The model is particularly suitable for the study of cyclodextrin as a stabilizing system for compounds that are sensitive to light, oxygen, temperature or the media which contain them.     

Pharmacokinetic curve fitting when the experimental error of the concentration-time data is represented by a relative error model

When the experimental error of concentration-time data is represented by the relative error model (i.e. constant coefficient of variation) two approaches (direct input of concentration-time data with 1/C2i as a weighting factor, and input of logarithmically transformed concentration-time data) are equally effective in pharmacokinetic modelling. Advantages of the latter approach are discussed.     

An application of nonlinear mixed-effects modeling to pharmacokinetic data exhibiting nonlinear and time-dependent behavior

A population pharmacokinetic (PK) analysis was performed on plasma concentrations of GW468816 observed in dogs after 10, 25, and 50 mg/kg/day repeated intravenous administration. A two-compartment model was fitted to the concentration-time data using the NONMEM program. Dose and time dependency of PK parameters was investigated. Selection of the best model was performed using a stepwise approach. A Michaelis-Menten elimination process was used to describe the PK dose dependency, whereas an interoccasion variability on V(m) (the maximum elimination rate of the Michaelis-Menten elimination process) was initially used to describe the time dependency of the PKs, and the final model included an exponential function to account for time variance on V(m). The K(m) value of the final model was 29.6 microg/mL, whereas V(m) was estimated to vary with time from 4.97 microg/h/kg at day 1 to a maximum mean value of 9.64 microg/h/kg at day 14. This approach can be applied to either rich or sparse data leading to estimates of individual parameters by using Bayesian feedback. The overall information obtained can be used to interpret toxicological and pharmacological endpoints and integrated with further in vitro-in vivo studies to supply a comprehensive PK behavior before the first time in human studies.     

Estimation of ligand binding parameters by simultaneous fitting of association and dissociation data: a Monte Carlo simulation study

A new procedure for analysis of ligand binding kinetics was evaluated by Monte Carlo simulations. In this, all association and dissociation data were fitted simultaneously to a set of nonlinear equations. This should have several advantages over more conventional methods; data are better used in a single fitting procedure in which the degrees of freedom are maximized and the error term is spread over more observations; all relevant parameters (Bmax, k1, and k-1) are obtained directly; values obtained from measurements are not treated as errorless; and it yields a single residual term that can be used for statistical comparison among binding models and/or experiments. We have compared this approach with the common practice of analyzing the association and dissociation phases separately, either by nonlinear regression or by linear regression after suitable transformations. With respect to both the precision and accuracy of parameter estimates, the simultaneous procedure was superior to the other two methods. The properties of the simultaneous procedure were further investigated, concerning both parameter estimation and the probability of reliably detecting a second binding site. For the latter, the relative density of receptor subtypes and the dissociation rate constants were found to be of major importance, whereas association rate constants and ligand concentration were of minor importance in this respect. The probability of resolving two sites by kinetic or equilibrium data under similar conditions with the aid of a single labeled ligand was examined. When the selectivity of the ligand was low, the resolution was found to be more probable when based on kinetic, rather than equilibrium, data. This was true at higher selectivities as well, provided kinetic data were obtained at two different ligand concentrations.     

吸附法纯化青霉素酰化酶

目的纯化发酵液中的青霉素酰化酶。方法采用吸附纯化法。结果按 1 2 % (W /V)的比例将皂土加到含青霉素酰化酶的发酵上清液中 ,可将 98%的酶吸附 ,而同时吸附的杂蛋白质仅占发酵上清液总蛋白质的 14 5 %左右。吸附过程受pH影响较大 ,在 pH 6 5～ 7 5时 ,吸附效果最佳。使用不同种类的缓冲液洗涤酶 -皂土复合物 ,发现缓冲液的种类对酶的洗涤影响不大。使用含5 0 %以上的PEG和 8 0 %的NaCl的磷酸缓冲液可以将酶全部洗脱。结论此法可在常温下操作 ,酶活力收率较高 ,具有潜在的工业应用价值     

释放分割法体外评价释放特征符合Higuchi方程的缓释制剂药物动力学

提出一种Higuchi释放缓释制剂药物动力学体外评价方法 ,将Higuchi释放以高斯 牛顿法分割成零级释放、一级释放和速释部分 ,每部分释放对体内药物动力学的贡献值则通过经典的药物动力学计算获得。方法学研究证明了释放分割法与基于零级释放药物动力学的剂量分割法效果相当 ,释放分割法计算得到的血药浓度 (CRD)与剂量分割法计算得到的血药浓度 (CDD)间的相关方程为CDD=-0 2 5 88+1 0 1 4CRD(r=0 993 6)。由于任意Higuchi释放曲线可以通过归一化的Higuchi释放曲线线性化表达 ,所以归一化Higuchi释放曲线的分割系数可作为非归一化的Higuchi释放的体外评价的模数。释放分割法可以对制剂的体外释放行为进行经济的评价 ,适用于缓释制剂的处方筛选、体内外相关性研究等     

吸附法纯化青霉素酰化酶的因素研究

按1．0％～1．2%（w／v）的比例将皂上加至青霉素酰化酶（产生菌株Bacillius subtilis BH97）的发酵上清液中，98％的青霉素酚化酶可被吸附，而吸附的蛋白质仅占发酵上清液的14．5％左右。吸附和洗脱过程受pH影响较大，在pH7．0～7．5时吸附效果最佳，而在pH6．5～7.5洗脱效果较好。不同种类的缓冲液洗涤酶-皂土复合物，受缓冲液影响不大。使用含5．0％以上的聚乙二醇和 8． 0％的 NaCl的磷酸缓冲液可将酶全部洗脱。此法简便易行，可在常温下操作，酶活力收率较高，可望具有一定的工业应用价值。     

The assessment of pharmacokinetic parameters of teicoplanin in burns comparing the methods of nonlinear curve fitting and quantified maximum entropy

The pharmacokinetics of teicoplanin in patients with severe burns has been assessed using two different numerical methods: a nonlinear curve fitting procedure and quantified maximum entropy. On the whole nonlinear curve fitting and quantified maximum entropy provided different pharmacokinetic parameter estimates for the same sets of data. With respect to correctness and reliability of the values, quantified maximum entropy appears to be the better approach. However, its full success depends on the data available. The data material need to be comprehensive to assure a maximum information content to be extracted. The nonlinear curve fitting approach requires less sophisticated mathematical modelling which is possible on common hardware, and produces results faster than quantified maximum entropy. Thus, nonlinear curve fitting is the method of choice if a rapid assessment of the data is required, whereas quantified maximum entropy should be the method of choice in research and development, where the required accuracy of the estimates is more important than time.     

The chorioallantoic membrane: A novel approach to extrapolate data from a well-established method

The chorioallantoic membrane (CAM) of the chicken embryo is a highly vascularized extra-embryonic structure that has been widely used as an in vivo model for the evaluation of angiogenesis. This study was designed to optimize data extrapolation from the most exploited experimental protocol to improve its efficiency and the reliability of the obtainable results. In our study, we followed the most common procedure for CAM assay, employing retinoic acid and vascular endothelial growth factor as standards. CAMs were photographed at t₀, t₂₄, and t₄₈; then, the main parameters of the predefined vascular network/area were evaluated. Subsequently, their variations in each CAM were calculated comparing them within the same CAM over the course of the whole treatment (t₂₄ and t₄₈), also comparing the treated CAMs respect to the untreated ones. Thus, we provide a novel approach aimed at extrapolating data from CAM assay that allows to (i) have a greater reliability and richness of data; (ii) better estimate the potential pro- and anti-angiogenic activity of new candidate drugs; (iii) save both eggs and time for the experiments.     

Application of adsorption method to the chromatographic analysis of free drug concentration

The development of analytical techniques for estimation of free drug concentration is crucial for the needs of modern pharmacology. Up to now, many different methods of free drug assay have been used. The methods involving isolation of free drug from a sample are most frequently applied because they can be easily adopted for the processing of real samples. Among the methods that do not require free drug isolation only the adsorption method could be promising in application to samples of this kind. The successful use of the adsorption method is possible only if two requirements are fulfilled: (I) the chosen adsorbent does not bind proteins from the sample and (II) the processes of adsorption of the assayed drug on the adsorbent used and on the protein should be independent. This paper discusses the possibilities of application of the adsorption method for determination of free drug concentration using propofol as the model drug. The presented results show that the fulfillment of the above conditions may be very difficult if not impossible not only for propofol, but for other drugs as well.     

Application of the transformed Potts-Guy equation to in vivo human skin data.

Data developed by Wenkers and Lippold for the flux of 10 nonsteroidal anti-inflammatory drugs from light mineral oil (MO) through human skin in vivo has been analyzed using the transformed Potts-Guy equation. The analysis shows that the flux is dependent not only on the solubility in MO (S(MO)), but also on the solubility in acidic water (S(AQ)). This dependence of flux on S(AQ) shows that the previously reported dependence of flux on S(AQ) from in vitro experiments using hairless mouse skin is not an artifact of the in vitro experiments but is due to a characteristic of the skin barrier. Further inspection of the equations used by Wenkers and Lippold in their analyses of their data shows that the equations are variations of the transformed Potts-Guy equation.